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Mechanism of methanol decomposition on the Pd/WC(0001) surface unveiled by first-principles calculations

Jinhua Zhang, Yuanbin She

《化学科学与工程前沿（英文）》 2020年第14卷第6期页码 1052-1064 doi: 10.1007/s11705-019-1908-y

摘要： In this study, the decomposition of methanol into the CO and H species on the Pd/tungsten carbide (WC)(0001) surface is systematically investigated using periodic density functional theory (DFT) calculations. The possible reaction pathways and intermediates are determined. The results reveal that saturated molecules, i.e., methanol and formaldehyde, adsorb weakly on the Pd/WC(0001) surface. Both CO and H prefer three-fold sites, with adsorption energies of ‒1.51 and ‒2.67 eV, respectively. On the other hand, CH O stably binds at three-fold and bridge sites, with an adsorption energy of ‒2.58 eV. However, most of the other intermediates tend to adsorb to the surface with the carbon and oxygen atoms in their sp and hydroxyl-like configurations, respectively. Hence, the C atom of CH OH preferentially attaches to the top sites, CHOH and CH O adsorb at the bridge sites, while COH and CHO occupy the three-fold sites. The DFT calculations indicate that the rupture of the initial C–H bond promotes the decomposition of CH OH and CH OH, whereas in the case of CHOH, O–H bond scission is favored over the C–H bond rupture. Thus, the most probable methanol decomposition pathway on the Pd/WC(0001) surface is CH OH → CH OH → -CHOH → CHO → CO. The present study demonstrates that the synergistic effect of WC (as carrier) and Pd (as catalyst) alters the CH OH decomposition pathway and reduces the noble metal utilization.

关键词： density functional theory methanol direct methanol fuel cells WC(0001)-supported Pd monolayer decomposition mechanism

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different dielectrics on environmentally conscious powder-mixed EDM of difficult-to-machine material (WC-Co

Jagdeep SINGH,Rajiv Kumar SHARMA

《机械工程前沿（英文）》 2016年第11卷第4期页码 374-387 doi: 10.1007/s11465-016-0388-8

摘要：

Electrical discharge machining (EDM) is a well-known nontraditional manufacturing process to machine the difficult-to-machine (DTM) materials which have unique hardness properties. Researchers have successfully performed hybridization to improve this process by incorporating powders into the EDM process known as powder-mixed EDM process. This process drastically improves process efficiency by increasing material removal rate, micro-hardness, as well as reducing the tool wear rate and surface roughness. EDM also has some input parameters, including pulse-on time, dielectric levels and its type, current setting, flushing pressure, and so on, which have a significant effect on EDM performance. However, despite their positive influence, investigating the effects of these parameters on environmental conditions is necessary. Most studies demonstrate the use of kerosene oil as dielectric fluid. Nevertheless, in this work, the authors highlight the findings with respect to three different dielectric fluids, including kerosene oil, EDM oil, and distilled water using one-variable-at-a-time approach for machining as well as environmental aspects. The hazard and operability analysis is employed to identify the inherent safety factors associated with powder-mixed EDM of WC-Co.

关键词： WC hazard and operability analysis (HAZOP) discharging aerosol concentration dielectrics powders

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超音速火焰喷涂WC涂层替代电镀硬铬：疲劳和摩擦磨损性能

周克崧,邓春明,刘敏

《中国工程科学》 2009年第11卷第10期页码 48-54

摘要：

以WC涂层在飞机起落架的应用作为研究背景，对300 M超高强钢基体上电镀硬铬和超音速火焰喷涂WC-17Co和WC-10Co4Cr涂层的疲劳及与结果表明，有WC涂层300 M钢的疲劳寿命与无涂层300 M钢的疲劳极限和过载下的疲劳寿命相当，WC涂层对300 M钢的疲劳寿命不会产生不良影响；而电镀硬铬使300 M钢的疲劳极限降低120 MPa，疲劳寿命则降低疲劳失效分析表明， WC涂层中的疲劳裂纹在界面上发生偏斜，转向沿界面扩展，因此对基体的疲劳寿命没有影响；而电镀硬铬中的的疲劳裂纹扩展到基体表面，显著降低基体的疲劳寿命。Al—Ni—Bronze合金的摩擦磨损表明，与电镀硬铬对磨时，Al—Ni—Bronze合金发生明显的磨损，同时因质量转移而导致电镀硬铬的质量显著增加；而WCWC涂层与Al—Ni—Bronze合金的磨损机理主要为磨粒磨损；电镀硬铬与Al—Ni—Bronze合金的磨损机理主要为黏着磨损。

关键词： 300 M钢超音速火焰喷涂 WC涂层电镀硬铬疲劳摩擦磨损

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Optimization of multi machining characteristics in WEDM of WC-5.3%Co composite using integrated approach

Kamal JANGRA, Sandeep GROVER, Aman AGGARWAL

《机械工程前沿（英文）》 2012年第7卷第3期页码 288-299 doi: 10.1007/s11465-012-0333-4

摘要：

Wire electrical discharge machining (WEDM) is a well known process for generating intricate and complex geometries in hard metal alloys and metal matrix composites with high precision. In present work, intricate machining of WC-5.3%Co composite on WEDM has been reported. Taguchi’s design of experiment has been utilised to investigate the process parameters for four machining characteristics namely material removal rate, surface roughness, angular error and radial overcut. In order to optimize the four machining characteristics simultaneously, grey relational analysis (GRA) coupled with entropy measurement method has been employed. Through GRA, grey relational grade has been computed as a performance index for predicting the optimal parameters setting for multi machining characteristics. Using Analysis of Variance (ANOVA) on grey relational grade, significant parameters affecting the multi-machining characteristics has been determined. Confirmatory results prove the potential of present approach.

关键词： tungsten carbide composite wire electrical discharge machining (WEDM) Taguchi method grey relational analysis (GRA) entropy measurement method

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Wide gap active brazing of ceramic-to-metal-joints for high temperature applications

K. Bobzin,L. Zhao,N. Kopp,S. Samadian Anavar

《机械工程前沿（英文）》 2014年第9卷第1期页码 71-74 doi: 10.1007/s11465-014-0291-0

摘要：

Applications like solid oxide fuel cells and sensors increasingly demand the possibility to braze ceramics to metals with a good resistance to high temperatures and oxidative atmospheres. Commonly used silver based active filler metals cannot fulfill these requirements, if application temperatures higher than 600°C occur. Au and Pd based active fillers are too expensive for many fields of use. As one possible solution nickel based active fillers were developed. Due to the high brazing temperatures and the low ductility of nickel based filler metals, the modification of standard nickel based filler metals were necessary to meet the requirements of above mentioned applications. To reduce thermally induced stresses wide brazing gaps and the addition of Al₂O₃ and WC particles to the filler metal were applied. In this study, the microstructure of the brazed joints and the thermo-chemical reactions between filler metal, active elements and WC particles were analyzed to understand the mechanism of the so called wide gap active brazing process. With regard to the behavior in typical application oxidation and thermal cycle tests were conducted as well as tensile tests.

关键词： wide gap active brazing nickel filler metals high temperature application WC Al₂O₃